1. Field of the Invention
The present invention relates to a production method of chlorinated polyvinyl chloride resin. More precisely, it relates to a production method of a chlorinated polyvinyl chloride resin which makes it possible to shorten the time for chlorination reaction without sacrificing the initial coloring and heat stability of the chlorinated polyvinyl chloride resin, thereby improving productivity thereof.
2. Prior Art
A chlorinated polyvinyl chloride resin (hereinafter, referred to as "CPVC") can be obtained by chlorination of a polyvinyl chloride resin (hereinafter, referred to as "PVC"). CPVC is characterized by having a heat resistance superior to that of PVC while keeping excellent properties of PVC, and therefore it is used for pipes, joints, industrial plates, sheet or the like wherein heat resistance is required.
However, CPVC is not good in heat stability compared with PVC, that is, it is easily decomposed by heat during a molding process, which makes a long duration molding process problematical or discoloration may occur particularly in a transparent molded product, or some other problems may occur.
Production methods of CPVC, wherein chlorine gas is blown into a aqueous suspension of PVC under beaming of a mercury lamp, have been disclosed in Japanese Laid-Open Patent Publications Sho 58-103507 (1983) and Sho 64-6002 (1989), for example. In these publications, it has been proposed to shorten the time for chlorination and thereby to improve the productivity. That is, it is described that the time for chlorination is shortened and consequently the productivity is improved mainly by increasing the intensity of the mercury lamp together with raising the temperature of reaction in a process of chlorination reaction.
However, in obtaining CPVC by these methods, because of the above-mentioned problems inherent in CPVC, that are the initial coloring problem in the molding process and the deterioration of heat stability, shortening the time for reaction significantly has not yet been achieved.
In other words, as a production method of CPVC, a method to shorten the chlorination reaction time and thereby to improve the productivity without sacrificing the initial coloring and the heat stability has not been proposed yet, as a matter of fact.